elixir for aspiring erlang developers
TRANSCRIPT
BACKGROUND
This presentation is aimed at students of the bachelors degree course Applied Computer Science who (almost) finished the course “Advanced Programming Concepts - Functional Programming with Erlang”
This presentation was created for the course “Independent Coursework” at the University of Applied Sciences Berlin.
Supervisor was Professor Dr.-Ing. Hendrik Gärtner
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ABOUT ME
Torben Dohrn
Master student at the University of Applied Sciences Berlin
.NET Developer at a small company
I did the “Advanced Programming Concepts” course around two years ago
Interested in different computer science topics
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GOALS OF THIS PRESENTATION
After this presentation you …
Know about the Elixir programming language and some differences to Erlang
Can read simple Elixir code
Are able to write a simple “Hello World” program in Elixir
Are able to write a simple “Hello World“ web site with Elixir and Phoenix
Can decide when to use Elixir and when not
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AGENDA
What is Elixir?
Erlang compared to Elixir
Elixir extras
Creating a Hello World app
Phoenix
Phoenix creating a Hello World site
Elixir or not Elixir
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WHAT IS ELIXIR?
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SHORT HISTORY
Started in January 2011 by José Valim, a Ruby on Rails core committer
As influential Ruby/Rails is to modern web development, it has architectural drawbacks
Memory consumption can be quite high (unicorn/unicorn-worker-killer)
Multi threading is generally avoided
Can be slow
To overcome the limitations José Valim tried to bring the joy of Rails to the Erlang VM
The idea of Elixir was born
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SELF-DISPLAY ON ELIXIR-LANG.COM
„Elixir is a dynamic, functional language designed for building scalable and maintainable applications.
Elixir leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain.“
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DYNAMIC
Similar to Erlang, Elixir is dynamically typed.
Also similar to Erlang there are function and type specifications.
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FUNCTIONAL
Elixir is a functional language.
You have all the good parts of Erlang (pattern matching, guards, immutable data) but some “more modern” syntax and good tooling.
No side effects
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SCALABLE
As Erlang code, Elixir code runs in lightweight execution threads (called processes) that are isolated (“share nothing“) and exchange information via messages.
Because of their lightweight nature one can have hundreds of thousands of processes on one machine.
Because of the isolation all processes can be garbage collected independently no system wide pauses.
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MAINTAINABLE
The combination of several aspects makes Elixir code maintainable:
- functional programming paradigm: Shorter, cleaner code
- tooling (mix, linter, Dialyzer)
- Testing (ExUnit, DocTests)
- Umbrella projects (Split your project in several smaller projects)
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ERLANG VM
Elixir gets compiled to Erlang bytecode (BEAM)
No overhead in call to Erlang functions
Using of Erlang tools (e.g. rebar integration)
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WEB DEVELOPMENT
Several Erlang webserver available (e.g. Cowboy, httpd)
Several web frameworks available (e.g. phoenix, relax)
Plug – Specification for modules between web applications
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EMBEDDED SOFTWARE DOMAIN
As Erlang runs on ARM platforms so does Elixir
Raspberry Pi, Beagle Board Black, AR Parrot Drone 2.0
Nerves-Project, bakeware: Cross compiling for different platforms
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ERLANG COMPARED TO ELIXIR
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ERLANG COMPARED TO ELIXIR
Erlang and Elixir share some similarities. Think of Erlang with some differences.
Some of these differences are shown in the following slides.
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A MORE “USED TO” APPROACH
In general the syntax was brought closer to “modern“ languages.
Expression terminators are gone – line break (or optional semicolon) instead of dot.
Functions from modules are called with dot syntax: String.reverse() instead colon string:reverse().
Functions parameters can have default values.
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OPERATORS
In comparison to Erlang, Elixir omits the two operators AND and OR.
The AND and OR operators in Elixir behave like the Erlang ANDALSO and ORELSE.
Other operators: Erlang Elixir Usage
=:= === Match operator
=/= !== Negative match operator
/= != Not equals
=< <= Less than or equals
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VARIABLES AND ATOMS
Erlang
Variables starts with uppercase letter.
Atom starts with lowercase letter.
Elixir
Variables starts with lowercase letter.
Atom starts with a colon.
Literals with uppercase letter are called atom aliases (and are atoms with the value “Elixir.XXX”).
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COMPREHENSIONS
Erlang
pyth(N) ->
[ {A,B,C} ||
A <- lists:seq(1,N),
B <- lists:seq(1,N),
C <- lists:seq(1,N),
A+B+C =< N,
A*A+B*B == C*C
].
Elixir
def pyth (n) do
for a <- 1..n,
b <- 1..n,
c <- 1..n,
a + b + c <= n,
a*a + b*b == c*c,
do: {a, b, c}
end
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MODULES AND FUNCTIONS
In Erlang you have to explicitly export a function to make it public.
In Elixir you have to define a function as private, otherwise it‘s public by default.
Anonymous functions are defined with fn() -> … end instead fun() -> …end
If you assign a anonymous function to a variable you have to call it with a .prefix
hello = fn() -> "world" end
hello.()
"world"
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IMMUTABLE DATA, YET REASSIGN IS POSSIBLE
All data is immutable, yet this is allowed:
The data is still immutable. You just change the meaning of the label “a”
“In Elixir, once a variable references a list such as [1,2,3], you know it will always reference those same values (until you rebind the variable).”
Dave Thomas – Programming Elixir
Implicit changing of the value isn’t possible.
a = "hello"
a = "world"
iex> a = "hello"
iex> SomeThing.magic(a)
iex> a
"hello"
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BINARIES
Erlang Elixir Usage
erl iex REPL
erlc elixirc Compiler
erl elixir Executable
(rebar) mix Build tool
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REPL
In Erlang if you want to define a module you need to create a file first and compile that file. In Elixir you can define modules directly in the REPL.
Short codes for working in iex
h(ModuleName) – HELP. Prints the documentation of the module (instead of the history).
c(FileName) – COMPILE. Compiles and loads file
r(ModuleName) – RELOAD. Compiles and loads file of ModuleName
i(variable, function, Module…) – INSPECT. Show the type and some info.
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ELIXIR EXTRAS
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MIX
Command line build and dependency tool
Various tasks are executed with mix
Tasks can be extended
mix new my_awesome_app – Create a new Elixir program
mix compile – Compiles the program in the current folder
mix release – An extended Task. Only available if exrm is included
mix phoenix.server – Starts a phoenix site in development mode
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PIPE OPERATOR |>
The pipe operator |> is syntactical sugar to create more comprehensive pipelines by reversing the “flow“ of data.
Pseudocode + execution order:
Trim(Reverse(To_upper(" Hallo")))
--3-(----2-(-----1---(---0---)))
The pseudocode on the left can be expressed with the pipe operator as following:
Expression Execution order
" Hallo" 0
|>To_upper 1
|>Reverse 2
|>Trim 3
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PIPE OPERATOR |>
The argument on the left side of |> is introduced as the first parameter of the function call on the right side.
The usefulness gets even more obvious if we have multiple parameter:
A(B(C(D("E"),"F"),"G","H"),"I")
Which parameter belongs to which function?
"E"
|>D
|>C("F")
|>B("G","H")
|>A("I")
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DOCTESTS
Did you ever encounter a well documented function where the documentation did not correspond to the function it self? Maybe a refactoring not taking the docs into account? Something like this?
@doc """
This function multiplies three
numbers
"""
def multiplyWithSeven(oneNumber)
do
oneNumber*7
end
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DOCTESTS
Doctests can help you with this situation.
On including examples, Elixir will create a unit test which will point the developer to inconsistencies between documentation and code.
@doc """
This function multiplies three numbers
iex> multipyThreeNumbers(2,2,2)
8
"""
def multiplyWithSeven(oneNumber) do
oneNumber*7
end
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DOCTESTS
The command mix test will fail because the not matching documentation.
To include Doctests, write in the documentation of the function
iex> functionName prefixed by four spaces.
In the next line you write the result.
Multiple examples are considered as one test if there is no empty line between them.
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PROTOCOLS
Constructs which allow Elixir to have polymorphism.
defprotocol Nice do
@doc "Returns true if Torben likes the type"
def nice?(data)
end
defimpl Nice, for: List do
def nice?([]), do: true
def nice?(_), do: false
end
iex> Nice.nice?([])
true
defimpl Nice, for: Map do
def nice?({}), do: true
def nice?(_), do: false
end
defimpl Nice, for: Integer do
def nice?(_), do: false
end
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CREATING A HELLO WORLD APPShowing some of the features
Not necessary the most useful
app…
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SING ALONG
Install Elixir - http://elixir-lang.org/install.html
Testing installation: iex / iex.bat (on Windows) IO.puts "Hello world"
Creating a new project: mix new hello_world
edit .\hello_world\lib\hello_world.ex
Compile mix compile
mix test
To execute, run iex –S mix
HelloWorld.sayhello()
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SING ALONG – HELLO WORLD
defmodule HelloWorld do
def sayhello do
IO.puts("Hello World")
end
end
We create a module HelloWorld(actually, mix new did that for us already).
In this module we create a function
sayhello which sends "Hello World"
to the console.
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SING ALONG – GETTING TEXT
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
IO.puts(message)
end
end
IO.puts put text to the console (or filesor what ever).
IO.gets gets text from the console.
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SING ALONG – LOOP
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
IO.puts(message)
sayhello
end
end
After outputting the text we simply callthe same function again.
No need for fully qualified name, aslong as we are in the same scope.
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SING ALONG – CALL ERLANG METHODS
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
message1 = :string.to_upper(to_char_list(message))
IO.puts(message1)
sayhello
end
end Here the Erlang built-in string:to_upper function is called. (Elixir built-in function is also available).
Because Erlang expects char_lists we have to convert our string to char_listbefore usage.
All Erlang built-in functions
are available.
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SING ALONG – REASSIGN VARIABLE (HERESY)
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
message = :string.to_upper(to_char_list(message))
IO.puts(message)
sayhello
end
end In Elixir you can.
The data is still immutable. You just change the label to a different value.
In Erlang we can‘t label
different values with the
same variable name.
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SING ALONG – TIDY UP
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
IO.puts(:string.to_upper(to_char_list(message)))
sayhello
end
end
Obviously we don‘t need theintermediate variable here.
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SING ALONG – EXTRACT FUNCTION
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
IO.puts(upper(message))
sayhello
end
def upper(message) do
:string.to_upper(to_char_list(message))
end
end
Even if our function is not long, it iseasier to maintain if you useseverall small functions instead of one big one.
(And I need the function for thenext slides…)
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SING ALONG – PIPE OPERATOR
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
message
|>upper
|>IO.puts
sayhello
end
def upper(message) do
:string.to_upper(to_char_list(message))
end
end
Instead of IO.puts(upper(message)) whichgets applied from inner to outer:
3(2(1))
We can use the pipe operator. The intent of of the function gets more clear this way.
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SING ALONG – DOCTESTS
defmodule HelloWorld do
def sayhello do
message = IO.gets("State your business“)
message
|>upper
|>IO.puts
sayhello
end
@doc """
Upcases text. What did you expect?
iex> HelloWorld.upper("Hallo")
‘HALLO’
"""
def upper(message) do
:string.to_upper(to_char_list(message))
end
end
Now we add documentation to the function
upper.
With the addition of an example not only a
developer knows how this use this function, the
compiler does as well.
mix test now executes this doctest as well
See mix test --trace for a more detailed
view
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PHOENIX FRAMEWORK
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WHAT IS THE PHOENIX FRAMEWORK?
Phoenix is a web framework written in Elixir and runs in the Erlang VM.
What is it good for?
HTML5 apps
API back ends
Distributed systems
Features:
Server side MVC
Real time support via channels
Precompiled templates
Fast
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FAST?
Request are measured in microseconds. For a reason.
The same site (dynamically rendered by Phoenix and as static HTML copy served by Apache) had notable speed differences:
Average response time:
Apache 900 microseconds
Phoenix 300 microseconds
My mini pseudo benchmark is not scientific significant! Improvements possible!
Virtual Machine: Ubuntu 14.04
Case A) Phoenix 1.1.1 + Elixir 1.2, Production release
Case B) Static copy of the Phoenix site served by Apache2
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FAST?
Apache2 Phoenix
665 05/Jan/2016 "GET / HTTP/1.1" 200
499 05/Jan/2016 "GET / HTTP/1.1" 200
1657 05/Jan/2016 "GET / HTTP/1.1" 200
998 05/Jan/2016 "GET / HTTP/1.1" 200
942 05/Jan/2016 "GET / HTTP/1.1" 200
1381 05/Jan/2016 "GET / HTTP/1.1" 200
23:18:34.611 [info] Sent 200 in 225µs
23:18:35.000 [info] Sent 200 in 206µs
23:18:35.406 [info] Sent 200 in 336µs
23:18:35.798 [info] Sent 200 in 221µs
23:18:36.167 [info] Sent 200 in 449µs
23:18:36.562 [info] Sent 200 in 174µs
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COMPONENTS I
Endpoint
Handles all aspects of the request up to the router
The glue between OTP and Phoenix
Router
Dispatches incoming requests to the correct controller
Applies pipelines (groups of plugs)
Controllers
Prepare data and send it to views
Invoke rendering via Views
Views
Render templates
Provide helper function for use in template
Templates
Markup with aforementioned helper functions
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COMPONENTS II
Channels
Manage sockets for soft-real time features.
Uses WebSockets or LongPolling
Similar to controllers but with bi-directional communication on persistent connection.
PubSub
Allows channel clients (ios, android, javascript, c#) to subscribe to topics
Plug
“Plug is a specification for constructing composable modules to build web applications”
Examples: Authentication, logging, preprocessing
Multiple plugs create a pipeline
Ecto
Database wrapper
Query composition
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FLOW OF DATA
An Endpoint receives a request which gets dispatched to the router
The router decides which controller (and action) handles this request (+ pipeline)
The corresponding controller action invoke the view
The view renders the templates
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ASSET BUILDING
Phoenix has a optional dependency to node.js because it uses brunch.io
Brunch.io is a asset build tool for web assets
It can execute various plugins but in the default configuration “only” joins all *.css and *.js files to app.css and app.js correspondingly to reduce the amount of request to the server.
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CREATING A HELLO WORLD SITE
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GETTING STARTED
Install phoenix (and node.js and Erlang and Elixir…) http://www.phoenixframework.org/docs/install
ation
Create a new Phoenix app in the current folder mix phoenix.new hello_world_site --no-ecto
Only at the first time usage Brunch.io gets downloaded
Test the installation mix test – executes the default tests
mix phoenix.server – starts the server
On http://localhost:4000 the default site is shown
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GREETINGS
Edit the template hello_world_site/web/templates/page/index.html.eex
Create markup with calling function in the div block with the class “jumbotron” <p><%= sayhello %></p>
The sayhello function will be defined in the page_view. Because all the templates in …/page/ get rendered from the “page_view” view, we don’t have to qualify the module name
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TEST OUR GREETINGS
Before implementing the greeting, lets create a test.
Edit the ~/test/views/ page_view_test.exs and write a test for the function:
Execute the test in the console with mix test
Obviously our test fails. Lets change that:
Edit the corresponding view: hello_world_site/web/views/page_v
iew.ex
Execute the tests again. It should run.
def sayhello do
"Hello World"
end
test "says hello" do
assert HelloWorldSite.PageView.sayhello
== "Hello World"
end
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GREETINGS IN ACTION
After starting the server with mix phoenix.server we can observe our change in the default page:
http://localhost:4000
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ELIXIR OR NOT ELIXIR? When to use Elixir. And when
not.
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SO WHEN SHOULD I USE ELIXIR?
You should consider Elixir when…
… you are curious
… you want to leverage the Erlang VM but are intimidated of Erlang
… you come from a Ruby background
… you program fast APIs
… you value a great community
You shouldn’t consider Elixir when…
… you program desktop apps
… you program mobile apps
… your working application is in Erlang. Elixir is not faster than Erlang.
… you need lots of libraries. Library support is not great yet.
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WHO IS USING ELIXIR?
Pinterest (Image curation)
Puppet Labs (Automation)
22cans (Games)
Undead labs (Games)
+ 42 additional companies regarding to this list:
https://github.com/doomspork/elixir-companies/blob/master/README.md
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COMMUNITY
The Elixir community is as far as I can tell great.
Core contributors answer on the mailing list (José Valim answered me in ~30 min)
Many Ruby developer consider Elixir the next big thing and therefore there is a lot of posts and actions on the web right now.
There are Meetups and Conferences in Berlin ElixirConf.eu 10.05 – 12.05.2016
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SUMMARY
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SUMMARY
In this presentation you saw an overview in Elixir, a programming language based on Erlang.
It shares a lot of traits with Erlang, yet feels more “used to” because of syntax an powerful tooling.
You saw the differences both languages have and two “Hello World” applications, one on the console and one as a Web project.
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WHAT I DIDN'T COVER
Sigils – handle textual representations (regex, string interpolation…)
Meta Programing with Macros – Write Elixir in Elixir
Umbrella Apps – Split big apps in smaller, independent tasks
Supervisor trees – Similar to Erlang, Elixir uses Supervisors to restart processes
Distributed tasks – You can send messages to processes on different nodes
Elixir on embedded devices – You can deploy your OTP app on embedded devices
Production deployment – exrm creates OTP releases. Phoenix can also be hosted
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ELIXIR FOR ASPIRING ERLANG DEVSTorben Dohrn
@nexusger
http://nexusger.de
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SOURCES
Elixir self-display http://elixir-lang.com
Drawbacks on Ruby/Rails https://medium.com/@kenmazaika/why-im-betting-on-elixir-7c8f847b58#.tnz88vbv8
Erlang on the Parrot Drone: https://www.youtube.com/watch?v=96UzSHyp0F8
Erlang code in Elixir and vice Versa: http://blakewilliams.me/posts/playing-with-elixir-and-erlang/
Elixir variables ARE immutable: http://stackoverflow.com/questions/29967086/are-elixir-variables-really-immutable
Companies using Elixir: https://github.com/doomspork/elixir-companies
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